In certain radio communication systems, when one communication apparatus sends a control message commanding another communication apparatus to execute a given control operation, the timing for starting the control operation is synchronized between the two apparatuses. Further, to achieve the synchronization of the start timing, the control start timing may be specified in the control message.
Standards for such radio communication systems include, for example, the IEEE 802.16 standards for which standardization is being promoted at the Institute of Electrical and Electronics Engineers (IEEE). The IEEE 802.16 standards provide that a radio frame number may be included as control start timing in a control message that a base station apparatus transmits to a mobile station apparatus. The radio frame number may be a sequence number appended to a radio frame of a prescribed period such as, for example, 5 ms.
Further, in the IEEE 802.16 standards, a MOB_SLP-RSP message to be used for the control of a sleep mode operation, for example, is defined as a control message for synchronizing the control start timing between the base station apparatus and the mobile station apparatus. The sleep mode operation is a mode of operation in which the mobile station apparatus temporarily suspends uplink and downlink transmissions while maintaining connection-related information. The MOB_SLP-RSP message carries as the control start timing the radio frame number of the radio frame at which the mobile station apparatus enters an unavailable interval.
FIG. 1 is a diagram illustrating one example of the sleep mode operation. At radio frame number N, the base station apparatus BS transmits the MOB_SLP-RSP message to the mobile station apparatus MS. The MOB_SLP-RSP message carries “N+2” as the radio frame number indicating the control start timing. Therefore, the mobile station apparatus enters the unavailable interval starting at the radio frame whose radio frame number is “N+2”. In the following description, the radio frame number indicating the control start timing may be referred to as the “start frame number” (SFN).
Certain radio communication systems employ retransmission request protocols. There are a variety of retransmission request protocols, but generally, when data is received correctly, the receiving end returns a positive acknowledgment (ACK) signal to the transmitting end. The transmitting end retransmits the data repeatedly until the positive acknowledgment signal is received or until a prescribed termination condition is satisfied.
For example, in the IEEE 802.16m standard currently under study in the IEEE 802.16 Working Group, the control message is transmitted by utilizing Hybrid Automatic Repeat Request (HARQ).
In the prior art, there is proposed a method for controlling an idle mode in a broadband wireless access communication system. The method includes the steps of: transmitting to a mobile station, by a base station, a de-registration command for commanding state transition to the idle mode; and transmitting, by the mobile station, a response message to the de-registration command. A count value increases each time the base station transmits the de-registration command, and the base station can retransmit the de-registration command until the count value reaches a preset maximum number of retransmissions. At the time of transmitting the de-registration command, starting by the base station a second wait timer to count a time to maintain connection information for the mobile station.
There is also proposed a method of retransmitting a data block through an HARQ. The method includes the steps of: retransmitting a data block through a HARQ by a preset maximum allowable number of times in a physical layer; retransmitting a data block through an HARQ by a preset number of times in a physical layer; reporting a reception of a NACK (Not ACKnowledgement) signal to a RLC layer when receiving the NACK signal by the maximum allowable number of times; and determining whether or not the data block is retransmitted. The method further includes receiving status report information through the physical layer, wherein whether or not the data block is retransmitted is determined on the basis of the status report information.
Related art is disclosed in Japanese National Publication of International Patent Applications No. 2008-524956 and No. 2009-521891.